"First and foremost, what we do works: we build strong brands. When we create strong brands, we create demand. When we create demand, we create growth," Weil said.

"When we create growth for brands, we create growth for companies. And we drive the economy forward. We drive jobs forward."

However, all too often, advertising agencies have failed to adequately demonstrate and communicate the results of the vital functions they perform.

"If we embrace data and we embrace technology, for the first time we will be able to prove - unequivocally - that what we do works. And, if we do that right as an industry, we're setting this up as a growth industry," said Weil.

As evidence of the need to convince brand owners about the value agencies provide, Weil quoted data from the Agency2020 report compiled by consultancy EffectiveBrands, and backed by the 4A's.

The study - presented at the conference - found that over half of US agencies believe they have "made the transformation in data and technology to drive ROI and improve our worth."

Less than a fifth of clients, though, shared this view. Such findings, Weil contended, "will help the 4A's drive the agenda of what it needs to do to support agencies."